The optical coherent and frequency-locked multi-carrier generation is one of the key techniques for the realization of superchannel, which is a promising candidate for future high-speed optical systems and networks. The flattened comb generation based on cascaded intensity modulator (IM) and phase modulator (PM) has been intensively studied and demonstrated. Recently, we have demonstrated flattened comb generation using only phase modulators driven by fundamental frequency sinusoidal sources with small frequency offset. Also, a lot of schemes for flattened comb generation have been demonstrated based on in-phase/quadrate (I/Q) modulator combined with recirculating frequency shifter (RFS). On the other hand, it is well known that relative to IM or PM, directly-modulated laser (DML) has the advantages of compact size, low power consumption and easy integration.